package com.weave.list;

/**
 * @Description 优化后的动态数组
 * @Author weave
 * @Date 2023/10/11 9:31
 */
public class ArrayList1<E> extends AbstractList<E>{
    /** 所有的元素 */
    private E[] elements;
    /** 存储首元素的位置 */
    private int first;
    private static final int DEFAULT_CAPACITY = 10;

    public ArrayList1(int capaticy) {
        capaticy = (capaticy < DEFAULT_CAPACITY) ? DEFAULT_CAPACITY : capaticy;
        elements = (E[]) new Object[capaticy];
        first = 0;
    }

    public ArrayList1() {
        this(DEFAULT_CAPACITY);
    }

    /**
     * 清除所有元素
     */
    @Override
    public void clear() {
        for (int i = 0; i < size; i++) {
            elements[i] = null;
        }
        size = 0;
        first = 0;
    }

    /**
     * 获取index位置的元素
     * @param index
     * @return
     */
    @Override
    public E get(int index) { // O(1)
        rangeCheck(index);

        return elements[index];
    }

    /**
     * 设置index位置的元素
     * @param index
     * @param element
     * @return 原来的元素ֵ
     */
    @Override
    public E set(int index, E element) { // O(1)
        rangeCheck(index);

        E old = elements[index];
        elements[index] = element;
        return old;
    }

    /**
     * 在index位置插入一个元素
     * 最好：O(1)  最坏：O(n)  平均：O(n)
     * @param index
     * @param element
     */
    @Override
    public void add(int index, E element) {
        rangeCheckForAdd(index);

        ensureCapacity(size + 1);

        for (int i = size; i > index; i--) {
            elements[i] = elements[i - 1];
        }
        elements[index] = element;
        size++;
    }

    /**
     * 删除index位置的元素
     * 最好：O(1)  最坏：O(n)  平均：O(n)
     * @param index
     * @return
     */
    @Override
    public E remove(int index) {
        rangeCheck(index);

        E old = elements[index];
        for (int i = index + 1; i < size; i++) {
            elements[i - 1] = elements[i];
        }
        elements[--size] = null;

        trim();

        return old;
    }

    /**
     * 查看元素的索引
     * @param element
     * @return
     */
    @Override
    public int indexOf(E element) {
        if (element == null) {
            for (int i = 0; i < size; i++) {
                if (elements[i] == null) {
                    return i;
                }
            }
        } else {
            for (int i = 0; i < size; i++) {
                if (element.equals(elements[i])) {
                    return i;
                }
            }
        }
        return ELEMENT_NOT_FOUND;
    }

    /**
     * 保证要有capacity的容量
     * @param capacity
     */
    private void ensureCapacity(int capacity) {
        int oldCapacity = elements.length;
        if (oldCapacity >= capacity) {
            return;
        }

        // 新容量为旧容量的1.5倍
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        E[] newElements = (E[]) new Object[newCapacity];
        for (int i = 0; i < size; i++) {
            newElements[i] = elements[i];
        }
        elements = newElements;

        System.out.println(oldCapacity + "扩容为" + newCapacity);
    }

    /**
     * 缩容
     */
    private void trim() {
        // 比如有30
        int oldCapacity = elements.length;
        // 通过右移1位做到除以2的效果：15
        int newCapacity = oldCapacity >> 1;
        if (size > (newCapacity) || oldCapacity <= DEFAULT_CAPACITY) {
            return;
        }

        // 剩余空间还很多
        E[] newElements = (E[]) new Object[newCapacity];
        for (int i = 0; i < size; i++) {
            newElements[i] = elements[i];
        }
        elements = newElements;

        System.out.println(oldCapacity + "缩容为" + newCapacity);
    }

    @Override
    public String toString() {
        StringBuilder string = new StringBuilder();
        string.append("size=").append(size).append(", [");
        for (int i = 0; i < size; i++) {
            if (i != 0) {
                string.append(", ");
            }

            string.append(elements[i]);
        }
        string.append("]");
        return string.toString();
    }
}
